Cryogenic method



July 11, 1967 (5 L P G 3,33QJ25 CRYOGENIC METHOD Original Filed Feb. 7, 1963 United States Patent @fitice 3,339,125 Patented July 11, 1967 3,330,125 CRYOGENIC METHOD Gustav Klipping, Berlin, Germany (Limastr. 38, Berlinlehlendorf, Germany) Original application Feb. 7, 1963, Ser. No. 257,015, new Patent No. 3,216,210, dated Nov. 9, 1965. Divided and this application Aug. 9, 1965, Ser. No. 478,398

Claims. (Cl. 62-555) This application is a division of application Ser. No. 257,015 filed Feb. 7, 1963, now Patent No. 3,216,210, granted Nov. 9, 1965.

Cryogenic technology provides temperatures below the boiling point of liquid gases (such as, for example, liquid helium, hydrogen, nitrogen, etc.) by allowing the liquid gas bath to boil under reduced pressure within a closed heat insulated vessel connected to an evacuation device. The temperature of the liquid gas bath is thus established by the vapor pressure prevailing above the liquid.

These cryostat devices as thus far known are particularly suited to cool test samples to a desired low temperature and maintain that temperature constant. For this purpose, the samples are introduced directly into the liquid bath or are held by a cooling finger in heat contact with the wall of the liquid bath container. Similar construction principles have been also utilized to provide deep cooling traps which are suitable for gas absorption in vacuum containers.

Such designs of cryostat devices have been very standard as far as shape and installation of the condensation surfaces are concerned because of the complexities involved in handling low pressure liquid gas baths. These designs prove very ineflicient and generally inadequate when the container surface is being used as a condensation surface for vacuum pumping operations because of the inherent difificulty involved in operating with low pressure liquid gas baths. For example, only the container wall surface in direct contact with the liquid bath is sufiiciently cooled to provide practical condensation and the area of this surface is continuously depleted as a result of the falling liquid level caused by the liquid gas evaporation. To eliminate this problem by continuously replenishing the supply of liquid gas is exceedingly difiicult because of the required low pressure operation and the extreme cold involved. Thus, most prior reduced pressure cryostat vacuum pumps have provided for large liquid volumes relative to the exposed cold surface so that the diminishing liquid level would produce a relatively small change in the surface area directly in contact with the cooling liquid. These designs have the obvious disadvantage of requiring relatively large, cumbersome liquid bath containers within the vacuum chamber for a given desired condensation surface area. In addition they provide poor cooling efficiency because the volume of coolant liquid is large relative to the useful condensation surface pumping area.

It is therefore the object of the present invention to provide a versatile cryostat apparatus which is continuous in its operation and which greatly reduces the necessary consumption of liquid coolant.

One feature of this invention is the provision of a cryostat device wherein cooling is provided by utilizing continuous evaporation of liquid gas from a heat insulated container vessel into a cold wall chamber maintained at a given low pressure.

Another feature of this device is the provision of a cryostat device of the above featured type including apparatus for continuously regulating the evacuation rate of the cold wall chamber so as to maintain the given low pressure.

Another feature of this invention is the provision of a cryostat device of the above featured type including apparatus for controlling the flow of coolant into the cold wall chamber in dependence upon the temperature of the chamber.

Another feature of this invention is the provision of a cryostat device of the above featured types wherein the fluid control apparatus is adapted to provide fluid flow into the cold wall chamber in dosed quantities so that the fluid evaporates in small droplets without the formation of a liquid bath.

Another feature of this invention is the provision of a cryostat device of the above featured types which includes apparatus adapted to produce a constriction in the coolant supply line to the cold wall chamber thereby providing a pressure drop through which the coolant liquid must ass. P Another feature of this invention is the provision of a cryostat device of the above featured type wherein the constriction is an adjustable valve.

Another feature of this invention is the provision of a cryostat device of the above featured type including apparatus for regulating the valve construction in dependence upon the temperature of the cold wall chamber.

Another feature of this invention is the provision of a cryostat device of the above featured types wherein the adjustable valve includes a by-pass opening the size of which can be pre-set to provide a continuous flow and a controlled opening which operates in dependence upon the temperature of the cold wall chamber.

These and other features and objects of the present invention will become more apparent upon a perusal of the following specification taken in conjunction with the drawing which is a schematic showing of a preferred embodiment of the invention.

Referring now to the figure there is shown a hollow cold wall chamber 1 located in a vacuum-tight housing In composed of base plate 2 sea-led to a pot-shaped upper part 3 by sealing gasket 3a. The housing In is evacuated through valve 4 set into the base plate 2.

Inserted into the base plate 2 are the vacuum jacket tubes 5, 6 and 7 opening towards the top, which encase respectively the connections for the temperature gauge 8a, positioned within cold wall chamber 1, the coolant feeder tube 9 communicating with the cold wall chamber 1, and exhaust-gas tube 10. The vacuum jackets 5, 6 and 7 are evacuated simultaneously with the inside of housing In via the valve 4.

Feeder tube 9 and vacuum jacket 6 lead into a siphon tube 11 including a vacuum jacket 12 which is attached, gas-tight, in the neck of liquid gas storage vessel 14 by means of flange connection 13. An annular bellows arrangement 13a has an end connected to the siphon tube 11, and another end sealed to vacuum jacket 6 by O-ring screw connection 15.

The siphon tube 11 has an upper portion which accommodates the feeder tube 9 and a lower portion of smaller cross section which extends into the liquid coolant 14a contained in the storage vessel 14. Positioned within the space between siphon tube 11 and vacuum jacket 12 is an elongated cylindrical valve assembly 16 closed at its lower end by a disc valve 16a positioned between the end of feeder tube 9 and the opening into the smaller lower portion of siphon tube 11. The upper portion of the cylindrical valve assembly 16 is supported by the valve actuating rods 16b which extend through and are sealed to movable bellows 13a. The disc valve 16a is provided with apertures which are closed by the lower end of vacuum jacketed feeder tube 9 upon movement into contact therewith.

Attached to the top and communicating with the cold wall chamber 1 is an exhaust-gas tube 10, enclosing the 3 chamber in a descending coil and the exhaust tube is soldered onto a base plate 19 and a rimmed top-plate 20 a i which straddles the cold wall chamber 1. Coiled tube 10,

cooled by the cold gas coming from cold wall chamber 1 and plates 19 and 20, in direct heat contact with coil 10, form a closed radiation protection around the cold wall chamber 1. The base plate 19 allows passage without direct contact of thermometer tube 8 and feeder tube 9 to the cold wall chamber. The cold wall chamber 1 is supported from the base plate 19 by the poorly heatconducting pins 21. The base plate 19 is supported by poor heat conducting pins 22 which are attached to base plate 2 of housing 1a.

The gas pressure temperature gauge 8a is connected to and controls the output of a signal generator 20a which provides electrical impulse energization for the cylindrical magnet winding 23 positioned around the bellows 13a. Located within and concentric with the winding 23 is a soft iron armature 160 which is attached to the valve supporting rods 16b.

Connected to exhaust-gas tube 10 outside the housing 1a is a pressure :gauge 24 showing the pressure prevailing inside of the cold wall chamber 1. Exhaust-gas tube 10 is connected with the evacuation vacuum pump 26 via flange connections 25 and 250. Between the flanges 25 and 25a is a bellows pressure regulator 28 adapted to seal the pump inlet pipe 27 in an expanded position and to allow gas flow therethrough in a contracted position.

The open end of bellows regulator 28 is connected by tubing 28a to a pressure gauge and to the vacuum pump inlet tube 27 through a valve 29. The exhaust tubulation 31 of the vacuum pump 26 is adapted for exhaust to atmosphere or for connection to a gas recovery apparatus.

In operation of thedevice a pressure is selected which 'will establish a desired equilibrium temperature within the cold wall chamber 1. With the valve open and the vacuum pump 26 operating this pressure is established 'within the tubing 28a as indicated by the pressure gauge 30. The valve 29 is then cQsedltQmaintain-this pressure 'withintlie tubing 23a. The bellows regulator 28 will then maintain this pressure in exhaust tube 10' and connected cold wall chamber 1. The bellows accomplishes regulation by expanding to seal off the vacuum pump 26 when the established pressure in tubing 28a is greater than that within exhaust tube 10 and by contracting to open tube 27 when the pressure in tube 10 rises above the established pressure in tubing 28a. 7 a

The magnet adjustment 17 is then used to position the winding 23 in such a way that, with winding 23 deenergized, the disc valve 16a will be supported slightly below the closed position defining a by-pass opening. The by-pass opening into feeder tube 9 thus established provides for a continuous flow of coolant into the cold wall chamber 1. The size of this by-pass opening is selected to pass a quantity of coolant not quite suflicient to establish the desired temperature within the cold chamber 1. The pressure sensitive temperature gauge 8a and signal generator device 29a are then used to control the magnet winding 23. With a higher than desired temperature within the cold chamber 1 the temperature gauge 8a causes the signal generator to supply an energizing current to magnet winding 23. The magnet energization produces a downward movement of the soft iron armature 160 which in turn lowers disc valve 16a via support rods 16!) and movmagnet winding 23 to provide an additional control openmg.

To maintain a desired temperature below the boiling point of the cooling medium the selected pressure and disc valve openings are such that the disc valve provides a pressure drop constriction in the coolant supply line. This in turn causes the coolant liquid to evaporate in super cooled droplet form into the feeder tube 9'and cool wall chamber 1. The cooled walls of chamber 1 can be either used to cool test samples or as a pump for the housing In by condensing gas molecules on its exterior surface. In the latter case a suitable dimensioning of the cool Wall chamber 1 and surrounding exhaust tube 10 can produce a good combination. For example, with liquid helium used as the coolant, the cool wall chamber can be main ature can pump nitrogen and other gases. 7

Thus the installation in accordance witlitliis invention operates on the basis of the evaporator principle, whereby the evaporating vessel is hollowrandipresents such a flow resistance that the freezing mixture carried to its inside in dosed quantities via the automatic control valves does not form a bath, but rather evaporates in tiny droplets. As a result of this design, the dimensions of the cooled wall may vary considerably and so may the shape of the device as well as its installation features, be open to a wide variety of choice and suitable to many specialized requirements. The installation is operated continuously; insuring safe operation, even over prolonged periods of time. Also, the temperature is automatically held constant. The apparatus operates with the best possible ef- ,7

ficiencyfactor of the freezing mixture, allowing the cooling of considerably larger surfaces with the same coolant quantity, as opposed to the designs known heretofore.

Obviously many modifications and variations of the present inventionare possible in light of the above teach- V tion means, providing a flow of the cryogenic coolant" into the cold wall chamber, regulating said coolant flowso as to cause instant evaporation of substantially all the coolant flowing into the cold wall chamber'thereby preventing the formation of a liquid coolant bath therein, and removing the evaporated coolant from the cold wall chamber with the evacuation means.

2. The method according to' claim 1 including the step of regulating the flow of the cryogenic coolant in dependence upon the temperature of the cold wall chamber.

3. The method according to claim 2 including the step of maintaining a constant below atmospheric pres- 7 sure in the cold wall chamber during the flow of the able bellows 1311. This downward movement of disc 7 valve la enlarges the opening into feeder tube 9 allowing the passage of more coolant to thereby reduce the temperature within cold chamber 1. When the temperature therein reaches the desired value the temperature gauge 8a a continuously open by-pass of given size and energized by cryogenic coolant. a

4. The method according to claim 1 including the step of maintaining a constant below atmospheric pressure in the cold wall chamber during the flow of the cryogenic coolant. V

S. The method according to claim 1 wherein said step of providing a flow of cryogenic coolant into the cold wall chamber comprises the steps of providing a continuous flow of cryogenic coolant into the cold wall chamber.

6. The method according to claim 5 including the step of regulating the fiow of the cryogenic coolant in dependence upon the temperature of the cold Wall chamber.

7. The method according to claim 6 including the step of maintaining a constant below atmospheric pressure in the cold wall chamber during the flow of the cryogenic coolant.

8. The method according to claim 5 including the step of maintaining a constant below atmospheric pressure in the cold wall chamber during the flow of the cryogenic coolant.

9. A method of providing a surface at cryogenic temperature with apparatus comprising an evacuable cold Wall chamber, liquid coolant supply means including a supply conduit adapted to provide a source of cryogenic coolant for the cold wall chamber, and evacuation means for evacuating the cold wall chamber, which method comprises the following steps:

evacuating the cold Wall chamber with the evacuation means; providing a fiow of the cryogenic coolant into the cold wall chamber through the supply conduit; regulating the coolant flow in the supply conduit so as to cause evaporation of the coolant liquid into super-cooled droplet form, to thereby cause instant evaporation of substantially all of the coolant flowing into the cold Wall chamber; and removing the evaporated coolant from the cold Wall chamber with the evacuation means.

10. The method according to claim 9 including the step of regulating the flow of cryogenic coolant through said supply conduit in dependence upon the temperature of the cold Wall chamber.

References Cited UNITED STATES PATENTS 3,216,210 11/1965 Klipping 62 X 3,252,291 5/1966 Eder 62 s5.5

OTHER REFERENCES LLOYD L. KING, Primary Examiner. 

1. A METHOD OF PROVIDING A SURFACE AT CRYOGENIC TEMPERATURE WITH APPARATUS COMPRISING AN EVACUATE COLD WALL CHAMBER, LIQUID COOLANT SUPPLY MEANS ADAPTED TO PROVIDE A SOURCE OF CRYOGENIC COOLANT FOR THE COLD WALL CHAMBER, AND EVACUATION MEANS FOR EVACUATING THE COLD WALL CHAMBER, WHICH METHOD COMPRISES THE FOLLOWING STEPS: EVACUATING THE COLD WALL CHAMBER WITH THE EVACUATION MEANS, PROVIDING A FLOW OF THE CRYOGENIC COOLANT INTO THE COLD WALL CHAMBER, REGULATING SAID COOLANT FLOW SO AS TO CAUSE INSTANT EVAPORATION OF SUBSTANTIALLY ALL THE COOLANT FLOWING INTO THE COLD WALL CHAMBER THEREBY PREVENTING THE FORMATION OF A LIQUID COOLANT BATH THEREIN, AND REMOVING THE EVAPORATED COOLANT FROM THE COLD WALL CHAMBER WITH THE EVACUATION MEANS. 